On a collision course

Two things are on a collision course if they are moving toward each other in a way that will result in a crash or a collision. Imagine one set of train tracks going north-south. One train is traveling northbound, but ten miles away another train is traveling southbound. They are on a collision course: if they keep moving in this way, they will collide. (The crash can be avoided if they change their movement.)

What would happen if an asteroid were on a collision course with the Earth? Specifically, what would happen if an asteroid were moving through space in a way that would cause a crash with Earth? NASA scientists tried to change the positioning of an asteroid in deep space. This was for practice. If an asteroid is ever on a collision course with the Earth, NASA wants to know it can change the asteroid’s trajectory.